The avian vocal control system provides a model for many aspects of neural integration, plasticity and learning. Songbirds learn their songs by imitating external models, and the major brain nuclei involved in vocal behavior have been identified. These nuclei are sexually dimorphic and develop under hormonal influence. I propose to explore the sensory-motor representation of a learned skill by studying the functional organization, physiological properties, anatomical connections and development of nucleus robustus archistriatalis (RA) , a nucleus on the motor pathway for song that is known to be essential for the ]production of learned vocalizations. The main experimental approaches will be: 1) Localizing areas in RA where electrical stimulation elicits song-like vocalizations; 2) mapping anatomical connections between RA and the respiratory system; 3) Recording neural activity in RA related to producing and hearing vocalizations in awake birds; 4) Determining the sources of auditory input to RA; and 5) Studying the development of connections between RA and other parts of the vocal system in young birds. These experiments use several approaches to examine how the motor skill of song is represented within a vocal control nucleus. The results will help to elucidate 1) how learned and unlearned components are combined to produce a complex behavior, 2) the way in which perceptual and motor aspects of a learned skill are represented in the brain, and 3) the way the structure of the brain develops under the influence of sensory-motor experience. A better understanding of the principles involved in this form of sensorimotor memory may in turn suggest cellular mechanisms that encourage or limit some forms of learning.